This invention relates to a process for making gypsum board having improved through-penetration strength. In particular, the invention relates to a process for encapsulating a fiberglass or plastic scrim (mesh) in a high density gypsum layer proximate the paper/gypsum layer interface. It is generally preferred to place the scrim at the back paper/gypsum layer interface. This process is particularly adapted to making a gypsum board having at least one face comprising a high density gypsum layer overlaying a lower density, foamed gypsum core. In accordance with the invention, a high density calcium sulfate hemihydrate slurry is placed between the back paper and the fiberglass or plastic scrim, forcing the slurry through the open mesh scrim, and thereby encapsulating the scrim with hemihydrate slurry and developing excellent bond between the paper, the high density gypsum layer and the foamed gypsum core.
In the gypsum wallboard industry, it is well known to manufacture gypsum board having at least one face comprise a layer of high density gypsum overlaying a lower density, foamed gypsum core. The high-density gypsum slurry has excellent adhesion with the paper sheet comprising the front face of the board and the low-density gypsum core.
Gypsum wallboard having a high-density layer on both faces has been commercially available for several years. However, it is desired to improve the through-penetration of the gypsum board and to improve further its abuse resistant properties. Fiberglass scrim and plastic scrim are materials that are known reinforcing agents in gypsum wallboard. These scrim materials are usually incorporated in the foamed gypsum core so as not to interfere with the bond between the paper facing sheets and the gypsum core.
It is an object of this invention to provide a process wherein a fiberglass scrim or plastic scrim is encapsulated in at least one high density gypsum layer in a gypsum wallboard between the facing paper and the low density, foamed gypsum core.
It is another object of this invention to provide a process wherein a high density calcium sulfate hemihydrate slurry is fed between a paper facing sheet and a fiberglass scrim or plastic scrim sheet and subsequently compressed wherein the scrim sheet is substantially encapsulated in the high density calcium sulfate hemihydrate slurry.
It is a further object of this invention to provide a gypsum wallboard having improved through-penetration strength.
These and additional objects and advantages of this invention will be readily understood from a consideration of the drawings and the following detailed description of the preferred embodiment.